Presently the apparatus used for measurement of air speed of a helicopter permits the obtaining of results giving a sufficient accuracy for average and high speeds, that is to say greater than 50 knots or substantially 25 m/s. These measuring apparatuses based on the principle of comparison of the dynamic pressure generated by displacement of the helicopter in the air and of the static pressure of this cannot pretend to permit establishment of the parameters of the vector speed of the helicopter, only the axial speed, in the longitudinal direction of the helicopter and in the front to rear direction of this being alone able to be determined. The replacement of these apparatuses by more complex apparatuses cannot be envisaged, these more complex apparatuses being reserved to fixed installations of test flight centres.